Microbiology Viral Structure & Multiplication
plaques
areas where virus-infected cells have been destroyed and show up as a clear, well-defined patches in the cell sheet
Prominent viral infections worldwide:
COVID19
Bacteriophage
"bacteria eating" -most contain double-stranded DNA, but some RNA types as well -every bacterial species is parasitized by various specific bacteriophages
In vivo
"in-life" laboratory-bred animals and embryonic bird tissues
Types of CPEs include
- Gross changes in shape and size - Development of intracellular changes - Inclusion bodies - Syncytia
regular lytic cycle steps
1.Adsoption: bacteriophage binds to the bacterial cell 2. Penetration: injects its nucleic acid. 3. Duplication: then nucleic acid is free within that cell, replicates its virus genetic material 4. Biosynthesis: assembly of new virions 5. Maturation 6. Lysis of weakened cell and release of viruses
Seawater can contain ___________ viruses per milliliter.
10 million
poliovirus-infected cell has ___________ virons
100,000
poxvirus-infected cell has ___________ virons
3,000 t0 4,000
herpesviruses completes replication cycle in
36 hours (longer)
poliovirus completes replication cycle in
8 hours (Fast)
Retroviruses turn their RNA genomes into
DNA
DNA viruses replication in human cells
DNA virus uses the DNA dependent DNA polymerase in host cells to replicate themselves. Process called transcription. Then virus uses the DNA dependent RNA polymerase to transcribe those genes. Then you get translation which gets you viral proteins.
Nucleic acid can be either ______ or _______, but not both.
DNA; RNA
Viruses are better described as ______ or _____ rather than alive or dead
active; inactive
DNA polymerase is
an enzyme that makes DNA. Going to make DNA molecules
RNA polymerase is
an enzyme that makes RNA. Going to make RNA molecules
DNA dependent DNA polymerase
an enzyme that uses DNA as the template for producing DNA (your cells use this to replicate)
what is polymerase?
an enzyme which brings about the formation of a particular polymer, especially DNA or RNA. Word in front of polymerase is what is going to be made
RNA viruses:
can be double-stranded, but more often are single-stranded
envelope
external covering of a capsid, usually a modified piece of the host's cell membrane
Viruses contain DNA or RNA, but ______ _______.
not both
Cells that lack compatible virus receptors (lock) are resistant to invasion of virus spikes (key). true/false
true
Cells that lack compatible virus receptors are resistant to adsorption and invasion by that virus. true/false
true
Easier to develop vaccines to prevent viral diseases. true/false
true
Even though viruses do not exhibit most of the life processes of cells, they can direct them, and thus are alive. true/false
true
Viruses have a specific host range. true/false
true
Viruses infect every type of cell. true/false
true
Host range is limited by
type of host cell receptors on cell membrane
RNA dependent DNA polymerase
uses RNA to make DNA (reverse transcriptase)
phases of the animal virus replication cycle:
Adsorption Penetration Uncoating Synthesis Assembly Release
Segmented RNA viruse
individual genes exist on separate pieces of RNA, transitional jumps have to occur
Properties of Viruses
-Hostile takeover of host cells to replicate -Lack enzymes for most metabolic processes -Lack machinery for synthesizing proteins
Primary purposes of viral cultivation:
-Isolate and identify viruses in clinical specimens. -Prepare viruses for vaccines. -Do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells.
Adeno-associated virus (AAV)
-Originally thought that it could only infect cells infected with the adenovirus -Now found to infect cells infected with other viruses
Basic structure of a virus consists of
-external coating (capsid proteins) -core containing one or more nucleic acid strains of DNA or RNA -sometimes one or two enzymes
Delta agent
-naked circle of RNA -expressed only in the presence of the hepatitis B virus -worsens the severity of liver damage
Viruses possess these characteristics
-ubiquitous -size range of 20 nm to 1,000 nm -not made of cells
Reverse transcriptase
-utilizes RNA to make DNA -enzyme that is restricted to the retroviruses because human cells do not ever convert RNA into copies of DNA
DNA viruses synthesis
1. Enter the host cell's nucleus and then takes over host cell's machinery. Uses this machinery to replicate it, and produce new viral proteins
T-even bacteriophage
Infect Escherichia coli (E.coli) icosahedral capsid head containing DNA central tube surrounded by a sheath collar base plate tail pins fibers
How were viruses discovered?
Louis Pasteur hypothesized that rabies was caused by a "living thing" smaller than bacteria
Infections with high mortality rates:
Rabies, AIDS, Ebola
RNA dependent RNA polymerase
Replicases that copy RNA. Humans don't make RNA in its nucleus, so any virus that needs it will have to have an enzyme that produces it for it
HIV only infects
T cells of humans
Lysogenic state in bacteria
The viral DNA molecule is inserted at specific sites on the bacterial chromosome. The viral DNA is duplicated along with the regular genome and can provide adaptive genes for the host bacterium. Doesnt always happen
Virion
a fully formed virus that is able to establish an infection in a host cell
Viruses that infect bacteria are called
bacteriophages
Spikes are found on
both naked and enveloped viruses
Synthesis
replication and protein production
obligate intracellular parasites
cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses bacteria cannot live outside the host cell.
Retroviruses
carry their own enzymes to create DNA out of their RNA ( i.e.HIV)
Enveloped viruses can bud from:
cell membrane, nuclear envelope, endoplasmic reticulum
In vitro
cell or tissue culture methods
Common causes of acute infections:
colds, hepatitis, chickenpox, influenza, herpes, warts
inclusion bodies
compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm
satellite viruses
dependent on other viruses for replication
The nucleic acid in a virus can be
dsDNA, ssDNA, dsRNA, ssRNA
Once a retrovirus has become positive sense with reverse transcriptase, what does it do?
enters the nucleus of a host cell to be treated as a DNA virus
Penetration through endocytosis
entire virus is engulfed by the cell and enclosed in a vacuole or vesicle
Direct fusion of the viral envelope with the host cell membrane:
envelope merges directly with the cell membrane, liberating the nucleocapsid into the cell's interior
Number of genes in hepatitis B virus?
four genes
syncytia
fusion of multiple host cells into single large cells containing multiple nuclei
If RNA virus is negative sense then it must
have own enzyme that converts it to positive before translation can occur
Hundreds of genes in some ____________
herpesviruses
Almost all antiviral drugs license so far have been designed to target one of the steps in the viral life cycle:
integrase inhibitor class of HIV drugs interrupts the ability of HIV genetic information to incorporate into the host cell DNA
host range
limited range of cells that a virus can infect
SARS-CoV-2 can infect
multiple cells in humans and some animals
-negative sense RNA
must be converted before translation can occur
Naked viruses consist only of a __________________
nucleocapsid
Viruses are
obligate intracellular parasites
Detection of Viral Growth in Culture
observation of degeneration and lysis of infected cells
pleomorphic
organisms that are variable in shape
Visible manifestation of cytopathic effects (CPEs)
plaques
Enveloped viruses are more flexible than the capsid so enveloped viruses are __________
pleomorphic
Pasteur proposed the term virus, which is Latin for __________
poison
Infections that cause long-term disability
polio, neonatal rubella
capsid
protein shell that surrounds the nucleic acid
The number of viral genes is
quite small compared with that of a cell
+Positive-sense RNA
ready for immediate translation
RNA viruses synthesis
replicated and assembled in the cytoplasm
retroviruses always come packed with a
reverse transcriptase
the number of viruses released by infected cells is variable, controlled by:
size of the virus health of the host cell
What allows viruses to dock with host cells (like SARS-CoV-2)
spikes
enveloped viruses
take a bit of the cell membrane when they are released from a host cell
nucleocapsid
the capsid together with the nucleic acid
Release of animal virus
the number of viruses released by infected cells
Viral Tropism
the spectrum of cells of a host that a virus may infect
genome
the sum total of the genetic information carried by an organism
An infectious viral particle is called a
virion
Assembly of animal viruses
virus is put together using "parts" manufactured during the synthesis process
cytopathic effect (CPEs)
virus-induced damage to the cell that alters its microscopic appearance
Words in front of dependent are
what that enzyme uses as a template